Copper seam



Patented Sept. 29, 1936 UNITED STATES PATENTQOFFICE 'COI'PER SEAL! Edmund H. Sheafl, Merrick, N. Y., assignor 'to National Lead Company, Jersey City, IN. 1., a

corporation of New Jersey No Drawing. Application October 16, 1933,

Serial 4 cmmi. (01. 108-13) 10 protection by paint.

The invention consists in the discovery that a copper roof seam wherein the copper surfaces are bonded together by a lead base solder of which the alloying component is cadmium. is

15 immune to the corrosion that occurs when bonds of other solder compositions are used, as for example the ordinary lead tin solder., The explanation of this immunity appears to be that the alloy compounds, which are formed between 20 the cadmium and the copper surface while the solder is fused and which remain in the bond, are electro-positive to the copper, as is also the cadmium itself, whereas the corresponding alloy compound of tin with copper is electro-negative 25 to copper notwithstanding that tin itself is electro-positive. The corrosion which results from galvanic action in the presence of atmospheric moisture as the electrolyte is thus, according to this invention, inhibited bythe combination with 80 the lead base of the solder, of an alloying metal which is not merely of itself electro-positive to copper, but of which its copper compounds are also electro-positive to copper. Cadmium is a metal of this order and alloys of it with lead,

85 approximating the eutectic, have melting points within the range which permits the manufacture of the copper seam by the .use of ordinary soldering irons.

I am aware that during the war, when tin was 4 practically unobtainable, cadmium was proposed as a possible substitute for it, in lead base solders, but so far as I am aware such cadmium-containing solder was not continued on the market and the character of the galvanic relation between copper and cadmium-copper compounds was not i at any time recognized as the remedy for the progressive deterioration of copper roofs.

* This-invention consists also in the further dis:

covery that the addition of a small percentage of i0 bismuth or zinc to the metals composing the bond does not result in the formation of electro-negative compounds therein, so that either or both of thesemetals may be present in the bond, if desired, to improve the adhesion.

The copper roof seam of this invention thus comprehends, specifically. the combination of the copper surfaces and a bonding layer ,therebetween. ll composed principally of lead alloyed with cadmium with which one or both of the metals bismuth and zinc may be used.

In general the cadmium alone or the cadmium .and bismuth together should be present in the range of 11% to 20% of the whole and the zinc up to about 0.75%. Examples of preferred proportions are as follows:

No. 2 No. a 15 Zinc when the bonding layer of the copper seam is constituted substantially according to either of the preceding formulae, the roof will be as durable adjacent the seams as in its other parts and its life as a whole will be greatly extended.

1 claim:-

1. A copper ,roof comprising united copper sheets exposed to the elements. the seam between "sheets comprising copper surfaces joined by a bonding layer of lead alloyed with cadmium in a proportion between 11% and'20% 2. A copper roof comprising united copper sheets exposed to the elements, the seam between sheets comprising copper surfaces Joined by a soldered bond of lead alloyed with cadmium in a proportion between 11% and 20% and containing also a small proportion of zinc.

8. A copper roof comprising united copper sheets exposed to the elements, the seam between sheets comprising copper suriaces'ioined by a soldered bonding layer of lead'alloyed with cadmium and bismuth collectively within the range 5 of 11% to.20%.

4. A copper roof comprising united copper sheets exposed to the elements, the seam between sheets comprising copper surfaces joined by a solder bond composed of lead alloyed with cad- 5 EDMUND H. SHEAR. 

